This Week in Sex is a weekly summary of news and research related to sexual behavior, sexuality education, contraception, STIs, and more.

Study: New Parents Experience Change in Sexual Desire

I’m not sure anyone with small children needed a peer-reviewed research study to tell them that in the first few months after the baby comes their sex lives and desire change dramatically, but now there is one. Researchers from the University of Michigan interviewed 114 partners of women who had given birth within the past seven years (most of the partners were men, but some were women) and asked about their sex lives when they had a newborn at home.

Previous studies had found that the mothers’ sexual desire dips after childbirth and suggested physical reasons such as hormones and “messy vaginas.” The partners’ dip, however, shows that social and relationship factors are involved as well. The most common reasons partners gave for their low sexual desire after the baby came home were fatigue, stress, too little time, and the baby’s sleeping habits. Factors such as vaginal bleeding and breastfeeding were lower on the list.

I’m guessing that any of you with new babies at home are saying something like “duh” at this point. Of course, that could also be because you’re so sleep deprived you can only utter one syllable at a time.

How Long Does Pregnancy Last, Really?

We are all used to the idea that pregnancy lasts nine months, though some of us who’ve experienced it are pretty convinced that it lasts much, much longer than that. The medical community has long said that the average pregnancy lasts 40 weeks—though the clock starts ticking at the start of a woman’s last menstrual cycle before conception, not the day of conception or the day of implantation. New research suggests that there is a lot more variation in the total number of days a woman is pregnant than we may have thought.

Researchers followed 125 women who were trying to get pregnant. Through urinalysis they were able to tell when these women ovulated—which was presumed to be the day of conception, since eggs only last about 24 hours—and the day the embryo implanted.

After excluding those babies who were born pre-term, the researchers still found a high variation in the length of pregnancy, ranging from 35 to 40 weeks from the day of conception to the day of birth or about 38 to 43 weeks from the day of a woman’s last menstrual period.

Though the researchers say this variation is surprising and may change how practitioners determine and explain due dates, some obstetricians say this is nothing new. Dr. Tomer Singer, a reproductive endocrinologist and infertility specialist at Lenox Hill Hospital in New York, for example, told LiveScience that he already tells women they could expect their pregnancies to last anywhere from 37 to 42 weeks (using last menstrual cycle as the start date). The study was also small and limited to women who were not having fertility issues.

Modern-Day Wet Nurse Advertises on the Internet

A classified ad in France for what amounts to a wet nurse has caught national attention. Apparently inspired by a new law making same-sex marriage legal, a woman near Paris is offering male couples with infants her breastfeeding services. The ad exclaims, “I am a young mother in perfect health, a trained nurse of 29, and I am renting my breasts to milk-feed infants.” For 100 euros (or about $130), the woman promises to breastfeed the baby up to ten times a day.

In France, it is illegal to sell breast milk, but lawyers for the website that posted the ad believe that selling this kind of a service is allowed. The woman who posted the ad told Reuters Paris (in a “conversation” held via its website) that she has received more than a dozen inquiries, but only half of them were legitimate. “The rest were perverts,” she said.